Thermal recording material

Abstract

It is provided with a thermal recording material having a support coated with a coating solution as a color developing layer. The color developing layer has a colorless dye precursor which is normally colorless or light-colored, and a developer which reacts with the dye precursor to cause color development thereof upon heating. The developer is a bisthiourea compound represented by, for example, a formula (A-2): ##STR1## and the thermal color developing layer contains no sensitizer. In the thermal recording materials of the present invention, substantially no color is developed at a temperature of 120° C. while color development can be caused in response to heating with a thermal head or a laser beam. The developed color on the material can be erased upon contacting with alcoholic solvents, depending on the thiourea compound contained in the color developing layer. After erasure of the image, the material can be used again for recording with a thermal head or a laser beam.

What is claimed is: 
     
       1. A thermal recording material which is heat stable at temperatures above 100° C. comprising a support coated with a coating solution as a color developing layer, wherein the color developing layer comprises a colorless dye precursor which is normally colorless or light-colored, and a developer which reacts with the dye precursor to cause color development thereof upon heating, and which layer does not contain a sensitizer for the dye precursor or for the developer, and wherein the developer is a bisthiourea compound represented by one of formulae (A-1) through (A-10): ##STR14## 
     
     
       2. A material as claimed in claim 1, wherein the dye precursor is 3-N,N-diethylamino-6-methyl-7-anilinofluoran. 
     
     
       3. A thermal recorded material comprising a thermal recording material according to claim 1, the material being subjected to recording to provide a recorded portion on one surface thereof, the surface being covered with a plastic film. 
     
     
       4. A material as claimed in claim 3, wherein the plastic film is laminated on the surface through thermal laminating. 
     
     
       5. The thermal recording material of claim 1 which is heat stable at temperatures of 120° C. to 160° C. 
     
     
       6. The thermal recording material of claim 1 which is heat stable at temperatures of 150° C. to 160° C. 
     
     
       7. The thermal recording material of claim 1 wherein the difference in Macbeth background value before and after exposure to heat at a temperature above 100° C. is 0.13 or less. 
     
     
       8. The thermal recording material of claim 1 wherein the difference in Macbeth background value before and after exposure to heat at a temperature of 150° C. to 160° C. is 0.13 or less. 
     
     
       9. The thermal recording material of claim 1 including a thermally applied protective laminate film. 
     
     
       10. A method for reversibly recording a thermal recording material comprising a support coated with a coating solution as a color developing layer, wherein the color developing layer comprises a colorless dye precursor which is normally colorless or light-colored, and a developer which reacts with the dye precursor to cause color development thereof upon heating and thereby to provide a recorded portion on the material, which method comprises the steps of thermally recording an image on the developing layer and erasing the recorded image by contacting the developing layer with an alcohol solvent and wherein the developer is a bisthiourea compound represented by one of formulae (A-1), (A-2), (A-4) and (A-10): ##STR15## 
     
     
       11. The method of claim 10 wherein the erased recording material is again used to thermally record an image. 
     
     
       12. The method of claim 10, wherein the dye precursor is 3-N,N-diethylamino-6-methyl-7-anilinofluoran. 
     
     
       13. The method of claim 10, wherein the recorded portion is erased with an alcoholic solvent containing one to four carbon atoms without affecting perservability and stability of a background. 
     
     
       14. A thermal recording material comprising a support coated with a coating solution as a color developing layer, wherein the color developing layer comprises a colorless dye precursor which is normally colorless or light-colored, and a developer which reacts with the dye precursor to cause color development thereof upon heating, the developer being at least one bisthiourea compound represented by the following general formula (I): ##STR16## wherein X, R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , and R 8  are each a lower alkyl group having from 1 to 6 carbon atoms, an alkoxy group having from 1 to 6 carbon atoms, a cyclohexyl group, a nitro group, a cyano group, a halogen atom or a hydrogen atom; Y is S or SO 2  ; and m is an integer of from 1 to 3. 
     
     
       15. A material as claimed in claim 14, wherein the compound represented by the general formula (I) is at least one selected from the group consisting of B-1, B-8, and C-1 ##STR17## 
     
     
       16. A material as claimed in claim 15, wherein the compound represented by the general formula (I) is a compound of B-1 ##STR18## 
     
     
       17. A material as claimed in claim 15, wherein the compound represented by the general formula (I) is a compound of B-8. 
     
     
       18. A material as claimed in claim 15, wherein the compound represented by the general formula (I) is a compound of C-1. 
     
     
       19. A material as claimed in claim 14, wherein the dye precursor is 3-N,N-diethylamino-6-methyl-7-anilinofluoran. 
     
     
       20. A thermal recording material which is heat stable at temperatures above 100° C. comprising a support coated with a coating solution as a color developing layer, wherein the color developing layer comprises a colorless dye precursor which is normally colorless or light-colored, and a developer which reacts with the dye precursor to cause color development thereof upon heating, and which layer does not contain a sensitizer for the dye precursor or for the developer and wherein the developer is at least one bisthiourea compound represented by the following general formula (I): ##STR19## wherein X, R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , and R 8  are each a lower alkyl group having from 1 to 6 carbon atoms, an alkoxy group having from 1 to 6 carbon atoms, a cyclohexyl group, a nitro group, a cyano group, a halogen atom or a hydrogen atom; Y is S or SO 2  ; and m is an integer of from 1 to 3. 
     
     
       21. The thermal recording material of claim 20 which is heat stable at temperatures of 150° C. to 160° C. 
     
     
       22. The thermal recording material of claim 20 wherein the difference in Macbeth background value before and after exposure to heat at a temperature of 150° C. to 160° C. is 0.13 or less. 
     
     
       23. A thermal recording material which is heat stable at temperatures above 100° C. comprising a support coated with a coating solution as a color developing layer, wherein the color developing layer comprises a colorless dye precursor which is normally colorless or light-colored, and a developer which reacts with the dye precursor to cause color development thereof upon heating, and which does not contain a sensitizer for the dye precursor or for the developer and wherein the developer is at least one bisthiourea compound represented by the following general formula (II): ##STR20## wherein X and Z are each a lower alkyl group having from 1 to 6 carbon atoms, an alkoxy group having from 1 to 6 carbon atoms, a cyclohexyl group, a nitro group, a cyano group, a halogen atom or a hydrogen atom; and m and n are each an integer of from 1 to 3. 
     
     
       24. The thermal recording material of claim 23 which is heat stable at temperatures of 150° C. to 160° C. 
     
     
       25. The thermal recording material of claim 23 wherein the difference in Macbeth background value before and after exposure to heat at a temperature of 150° C. to 160° C. is 0.13 or less. 
     
     
       26. A material as claimed in claim 23, wherein the compound represented by the general formula (II) is at least one selected from the group consisting of D-1 and D2 ##STR21## 
     
     
       27. A material as claimed in claim 23, wherein the dye precursor is 3-N,N-diethylamino-6-methyl-7-anilinofluoran. 
     
     
       28. A thermal recorded material comprising a thermal recording material according to claim 14 or 23, the material being subjected to recording to provide a recorded portion on one surface thereof, the surface being covered with a plastic film. 
     
     
       29. A material as claimed in claim 28, wherein the plastic film is laminated on the surface through thermal laminating.